This invention relates to reactors for polymerizing, in a continuous throughput polymerizable materials in a liquid medium. Processes have been evolved for the continuous polymerization of monomers, such for example as processes described in Canadian Pat. No. 1,220,777, overcoming the more costly cumbersome procedures involved in batch processing. Such improved processes have, however, been limited to relatively small throughputs due in particular to the problem of dissipating the heat of the exothermal reaction in sufficient quantity in a given time span for precision control of critical reactor temperatures.